In application of touch panels, conventionally, as a position detecting method, there are employed various systems such as resistance film system and capacitance system. Of these, there has been a tendency of increasing the growth of resistance film system because of simple structure and advantageous cost performance. The touch panel structure using the resistance film system usually comprises a transparent conductive laminate and a transparent conductive glass having a thin film, which are placed opposite through a spacer, so that an electric current is applied to the transparent conductive laminate and a voltage in the transparent conductive glass having a thin film is measured. Namely, there is applied a principle where the transparent conductive laminate is contacted to the transparent conductive glass having a thin film when pushing thereof by a finger or a touch pen, and thereby an electric current is passed to the contacting part so that the position of contacting part is detected. As the application using the resistance film system, there are exemplified an automated teller machine and a display of train ticket machine.
The above transparent conductive laminate is a laminate having a conductive thin film which is formed on a film substrate. On the transparent conductive laminate, usually a hard coat layer is provided for the purpose of improving the transparency and withstanding the pushing operation in use of the touch panel.
In the touch panel production process, the transparent conductive polyester film having a thin film and the polyester film having a hard coat layer are attached through an adhesive layer (for example, refer to Patent Document 1), there is a problem that oligomers contained in the polyester film (usually an oligomer means a low molecular compound having cyclic trimer structure) are precipitated and crystallized on the surface of film causing to ingress of oligomers into the adhesive layer used for the adhesion of films so that the adhesive layer is deformed (for example, refer to Patent Document 2).
As a method of preventing the above oligomer precipitation, for example, there is proposed a method that a curable resin layer comprising a silicone resin and an isocyanate-based resin is provided on the polyester film deformed (refer to Patent Document 3). However, since the curable resin layer is formed by thermal curing, a heat treatment at a high temperature for the dissociation of the isocyanate-based resin and blocking agent is required so that much care in handling thereof is required because curls and slacks highly occur in the processing.
Therefore, when attaining reduction of the amount of oligomer precipitation by the method using the coating layer, it has been required that the coating layer has more excellent heat resistance than the generally known one, has an excellent transparency itself and has an excellent oligomer sealing ability.
Especially, in touch panel applications, recently, it tends to increase mounting them on communication and information equipments such as mobile phone and PDA (personal digital assistance), game machines or the like. With the market growth of these applications, it is required that they have more excellent transparency than the generally known one.
Under these circumstance, in the polyester film used in these applications, deterioration of visibility with increasing haze thereof after processing becomes an increasingly seriously problem.
As the way to solve the above problem, for example there is proposed a method of providing a hard coat layer on the polyester film for the purpose of preventing the oligomer precipitation. In this way, especially in case of applying and forming hard coat layers on both surfaces of film, the ability of preventing the oligomer precipitation is good. However, in this way, there is a problem that when winding the film as a shape of roll, the sliding property of film surface is deteriorated.